This invention relates to a cryosurgical probe. It relates more particularly to method and means for limiting and controlling the size of the freeze zone at the probe tip.
Cryosurgical probes are finding wider application in various types of surgical procedures such as correcting retinal detachments, removing cataracts, treating cervicitis, cervical erosion, cysts, etc. Basically, the probe comprises a handle with a hollow thermally-conductive tip protruding from the handle. A small diameter conduit extending through the handle to the probe tip conducts fluid refrigerant to the tip. As the refrigerant leaves the supply conduit, it cools by expansion, evaporation, and by the Joule-Thompson effect depending upon the type of refrigerant and its phase. The cooled refrigerant, in turn, cools the walls of the tip to a temperature low enough to freeze human tissue. The refrigerant exhausts from the tip through an exhaust conduit extending through the handle and leading ultimately to the atmosphere.
When used for cataract removal, for example, the probe tip is placed in contact with tissue, the tissue becomes frozen and adheres to the tip so that the tissue can be pulled away. Also, if the tip is held in contact with the tissue for a sufficient period of time, scar tissue forms to "weld" tissue together. The mending of a detached retina is accomplished this way.
Further, some probes includes provision for rapidly heating the probe tip electrically or by flowing warm fluid through the tip following a surgical procedure so that the tip can be released quickly from the tissue.
The probe tips assume a variety of sizes depending upon their purpose. Opthalmic probes, for example, have a straight or curved prove tip on the order of 0.070 inch in diameter and from 1/2 to 1 inch long. Other probes such as those used in gyneocological procedures have tips which are as large as 1 inch in diameter and several inches long. As a general rule, however, only the very tip end is used to freeze tissue during an operation. Unfortunately, with conventional probes, the entire tip freezes. In some cases, even metallic parts above the tip become cold. Unavoidably, then, portions of the probe other than the working end of the tip contact tissue not in the target area thereby freezing it and causing pain and possible injury to the patient.
One suggested solution to this problem has been to make the tips shorter so that they have less area to contact tissue. However, unless the tip projects an appreciable distance from the handle, it is very difficult to insert the tip end sufficiently and position it on the target tissue. Accordingly, prior probes still have this disadvantage.